Hydraulic expansion chuck

ABSTRACT

The invention relates to a hydraulic expansion chuck having an end on the tool side; and an end on the machine side. A shaft is disposed on the end on the machine side for clamping the expansion chuck in a machine tool. An expanding bushing is disposed on the end on the tool side and surrounded by a pressure chamber and can be radially deformed for clamping a tool under the action of a pressure medium received in the pressure chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulic expansion chuck for clamping in atool, in particular a drill or milling cutter.

2. Description of the Related

A chuck serves to connect a rotationally driven tool to the drivespindle of a machine tool. A chuck therefore has a pronounced chuckaxis, about which the chuck and the tool which is clamped therein arerotated during operation. In the direction of this chuck axis, a chuckalways has a tool-side end which is provided for receiving the tool anda machine-side end which is configured for connecting the chuck to thedrive spindle of the machine tool. At the machine-side end, a chuck ofthis type as a rule carries a conical shaft, in particular a steepshaft, what is known as an HSC (hollow shaft cone) shaft or the like.

What are known as the hydraulic expansion chucks form a category knownper se of chucks. In an expansion chuck of this type, the receptacle forthe tool is formed by a thin-walled expansion bushing. The expansionbushing is surrounded by a pressure chamber which is filled with apressure medium, for example an oil. The expansion bushing is configuredin such a way that, if pressure is applied to the pressure medium, it iselastically deformed radially and in the process clamps in the insertedtool. A hydraulic expansion chuck has the advantage, in particular, thatit damps jolts and vibrations which occur during operation. As a result,a particularly high surface quality and a long service life of the toolare achieved during machining.

WO 2005/097383 has disclosed a hydraulic expansion chuck of this typewhich can advantageously be used, in particular, in mold and dieconstruction and has a long and narrow design which is required for thispurpose. The known expansion chuck has a basic body which carries, atits tool-side end, the shaft which is provided for clamping theexpansion chuck in the machine tool. An approximately bell-shapedclamping sleeve which is drawn out at the free end to form an elongateand narrow neck region is placed onto the basic body on the tool side.Here, a thin-walled and hollow-cylindrical projection of the basic bodyextends within the clamping sleeve as far as its free end, the pressurechamber being formed at this end between the projection of the basicbody and the clamping sleeve. Here, the expansion bushing is formed inthe inner region of the basic body, which inner region adjoins thepressure chamber. Here, a narrow annular gap which is concentric withrespect to the chuck axis is formed between the outer circumference ofthe basic body and the clamping sleeve, which annular gap, as a pressuretransfer channel, connects the pressure chamber to a pressure generationunit, the latter being accommodated in a widened, machine-side sectionof the clamping sleeve.

The known hydraulic expansion chuck is advantageous for producing verylong, narrow chuck designs. However, the production of the expansionchuck is comparatively complicated. This relates, in particular, to theproduction of the thin-walled projection of the basic body and thepressure-tight soldering of the clamping sleeve to the basic body.

DE 100 07 074 A1 has disclosed a further expansion chuck. Said expansionchuck comprises a single piece basic body, on the machine-side end ofwhich once again a shaft is formed, while the tool-side end of the basicbody forms a clamping sleeve. Here, an inner sleeve which is separatefrom the basic body, and therefore also from the clamping sleeve, isinserted into the clamping sleeve, which inner sleeve contains anexpansion bushing and delimits, on the inner side, a pressure chamberwhich surrounds it. At its tool-side end, the inner sleeve is providedwith an outwardly protruding annular collar which overlaps with theclamping sleeve. Here, the annular collar extends over part of theradial width of the clamping sleeve which surrounds the annular collaron the outside. The interface which is formed between the annular collarand the clamping sleeve otherwise opens into the tool-side end face ofthe expansion chuck.

SUMMARY OF THE INVENTION

The invention is based on the object of specifying an improved hydraulicexpansion chuck which is advantageous, in particular, for realizing longand narrow designs.

According to the invention, this object is achieved by the features ofclaim 1. The expansion chuck according to the invention comprises atool-side end and a machine-side end, a shaft for clamping the expansionchuck in a machine tool being arranged at the machine-side end, and anexpansion bushing being arranged at the tool-side end, which expansionbushing is surrounded by a pressure chamber and can be deformed radiallyto clamp in a tool under the action of a pressure medium which isaccommodated in the pressure chamber. The machine-side end of theexpansion chuck is formed by a basic body which also carries the shaftand to which, on the tool side, a clamping sleeve which adjoins thepressure chamber on the outside is attached rigidly.

According to the invention, an inner sleeve is inserted into theinterior of the clamping sleeve, which inner sleeve is manufactured as aseparate component and is therefore not integrally connected to eitherthe clamping sleeve or the basic body. Said inner sleeve contains theexpansion bushing and delimits the pressure chamber on the inside. Atits tool-side end, the inner sleeve is provided with a radiallyoutwardly protruding annular collar, by way of which the inner sleeveoverlaps with the clamping sleeve in the radial direction. The annularcollar is therefore designed in such a way that it protrudes beyond theinner circumference of the clamping sleeve.

The substantially three part production of the expansion chuck (in theform of the basic body, the clamping sleeve and the separate innersleeve) is substantially simplified in terms of manufacturing technologyin comparison with the known solution, in which a projection which isconnected integrally to the basic body is provided instead of theseparate inner sleeve. The pressure-tight soldering of the expansionchuck at the machine-side edge of the pressure conducting region is alsosimplified substantially as a consequence of the three piece design,especially since the machine-side part of the clamping sleeve and of theinner sleeve which pushed into it is directly accessible before mountingof the basic body. At the same time, the connecting point between theclamping sleeve and the inner sleeve is protected by the annular collar,by way of which the inner sleeve overlaps the clamping sleeve at themachine-side end of the expansion chuck. In particular, damage to thisconnecting region as a result of friction with chips, or the like isavoided effectively.

In order to make the expansion chuck particularly insensitive to chipabrasion, the annular collar extends over the entire width of theclamping sleeve. Here, the annular collar terminates approximatelyflushly with the outer circumference of the clamping sleeve, inparticular on the outside. As a result, an interface formed between theclamping sleeve and the inner sleeve on the outer side of the expansionchuck does not open axially, but rather radially at the outercircumference of the expansion chuck. As a result, the transport ofchips takes place approximately perpendicularly with respect to theouter region of the interface, as a result of which the chips can exerta comparatively low force on the chuck material in the opening region ofthe interface.

In order to improve the protective effect, in one advantageousembodiment of the invention, in longitudinal section through theexpansion chuck, the annular collar is provided with an at least twostep contour which bears sealingly with a complementarily shaped recessagainst the tool-side edge of the clamping sleeve. As a consequence ofthis contour, an interface is therefore formed in the region of theannular collar between the clamping sleeve and the inner sleeve, whichinterface is kinked at least twice in longitudinal section, inparticular in each case by approximately 90°, approximately in themanner of a labyrinth seal. Here, at least in a part region of theinterface, the clamping sleeve is connected to the inner sleeve with amaterial-to-material fit, namely is preferably soldered, in particularbrazed.

A particularly stable connection of the clamping sleeve to the innersleeve is achieved as a consequence of the “labyrinthine” profile of theinterface and as a consequence of the annular collar which protrudesbeyond the clamping sleeve. This connection is stable both against thepressures which act from the inside, that is to say from the pressurechamber, and against the loads which act from the outside on thetool-side end of the expansion chuck, namely, in particular, the axialpressure which is transmitted from the tool to the inner sleeve,including the vibrations which occur during operation of the expansionchuck. In addition, the connecting face is also protected effectivelyagainst the abrasion forces as a result of chips, which abrasion forcesare exerted on the tool-side end of the expansion chuck from theoutside.

The clamping sleeve preferably has a through hole which penetrates theinner sleeve completely. The inner sleeve is preferably even lengthenedin comparison with the length of said through hole and thereforeprotrudes beyond the machine-side end of the through hole. The innersleeve therefore engages in a positively locking manner into the basicbody which adjoins the clamping sleeve on the machine side.

In order to generate a pressure which deforms the expansion bushinghydraulically, the chuck expediently has a pressure generation unitwhich is arranged offset axially with respect to the expansion bushingand the pressure chamber which surrounds it. In order to transmit theapplied pressure over the axial distance between the pressure chamberand the pressure generation unit, the expansion chuck contains apressure conducting system which is advantageously formed by anannularly closed gap or channel which is arranged concentrically withregard to the chuck axis.

In comparison with a customary hole as pressure conducting system, anannular gap with a comparable cross-sectional area has a generallysubstantially smaller radial extent. An annular gap with a sufficientcross-sectional area for pressure transmission can therefore also beattached in a space-saving manner in the case of an extremely narrowexpansion chuck. Moreover, the stresses introduced under pressureapplication into the material of the chuck in the region of the annularpressure conducting system are always rotationally symmetrical withregard to the chuck axis, with the result that no asymmetricaldeformation of the expansion chuck can occur and therefore the truerunning of the expansion chuck during operation is not impaired.

An annular and concentric pressure conducting system is particularlysimple to produce using the three part production of the expansionchuck, in which the annular gap is formed between the inner sleeve andthe clamping sleeve.

A geometry of the expansion chuck which is advantageous with regard tosaving space is achieved by the fact that the pressure generation unitis arranged in the clamping sleeve. Here, a pressure generation unitwith a piston/cylinder system is advantageous both with regard to simpleproduction and with regard to a simple handling capability of theexpansion chuck. Said piston/cylinder system comprises a pressure pistonwhich is guided in a cylinder bore or a sleeve which is optionallyinserted into a bore of this type. Simple filling of the pressurechamber of the pressure conducting system and of the pressure generationunit with the pressure medium is achieved by a filling hole which isangled away from the cylinder bore and connects the cylinder bore to thepressure conducting system. In one particularly simple and effectiverealization, the pressure piston can be actuated by means of a clampingscrew.

In one design of the expansion chuck according to the invention which isadvantageous, in particular, for mold and die construction, the clampingsleeve is drawn out on the tool side to form an elongate, narrow neckregion, the axial length of which is at least four times its externaldiameter. In particular, the length of the neck region is at least 100mm.

In one advantageous refinement, the radial extent of the annular gap isat most 0.2 mm, preferably approximately 0.1 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text, one exemplary embodiment of the invention will bedescribed in greater detail using a drawing, in which:

FIG. 1 shows a perspective illustration of a hydraulic expansion chuckfor clamping in a tool,

FIG. 2 shows a side view of the expansion chuck according to FIG. 1,

FIG. 3 shows, in a longitudinal section according to FIG. 2, theexpansion chuck there,

FIG. 4 shows an enlarged illustration of a detail IV from FIG. 3,

FIG. 5 shows, in a cross section V-V according to FIG. 2, the expansionchuck there, and

FIG. 6 shows an enlarged illustration of a detail VI from FIG. 5.

Parts and variables which correspond to one another are always providedwith identical designations in all the figures.

DETAILED DESCRIPTION OF THE INVENTION

The (hydraulic) expansion chuck 1 shown in various illustrations inFIGS. 1 to 6 serves to clamp in a rotationally driven tool (not shown),in particular a drill or milling cutter on the drive spindle of amachine tool (likewise not shown). The expansion chuck 1 is ofsubstantially rotationally symmetrical configuration with regard to achuck axis 2 which forms the rotational axis, and has a tool-side end 3and a machine-side end 4 as viewed in the direction of said chuck axis2. In the vicinity of the tool-side end 3, the expansion chuck 1 isdrawn out to form an elongate and narrow neck region 5 which has areceptacle 6 for the tool on the free end side, that is to say at thetool-side end 3).

Here, the axial length L (FIG. 2) of the neck region 5 is four times tofive times its external diameter D (FIG. 2). In a preferred size, thelength L of the neck region is approximately 100 mm in the case of anexternal diameter of 20 mm and an internal diameter d of the receptacle6 of 12 mm. However, an even longer and/or narrower design of theexpansion chuck 1 or an even lower internal diameter d can also berealized. The machine-side end 4 is provided with a shaft, for exampleconfigured as an HSC shaft (called fastening cone 7 in the followingtext), for connection of the expansion chuck 1 on the drive spindle.

As can be seen, in particular, from the sectional illustration accordingto FIG. 3, the expansion chuck 1 is substantially configured in threepieces. It comprises a basic body 8 which forms the machine-side part ofthe expansion chuck 1 and on which the fastening cone 7 is also formed.Furthermore, the expansion chuck 1 is formed from an approximatelybell-shaped clamping sleeve 9. The clamping sleeve 9 is placed with awidened annular region 10 onto the tool-side end of the basic body 8.The clamping sleeve 9 tapers in a stepped manner toward the tool-sideend 3 of the expansion chuck 1 in order to form the narrow neck region5. In its interior, the clamping sleeve 9 has a through hole 11 which isconcentric with respect to the chuck axis 2. As third constituent partof the expansion chuck 1, an inner sleeve 12 (FIG. 2) lies in thisthrough hole 11, which inner sleeve 12 penetrates the through hole 11over its entire length and projects beyond the machine-side end of saidthrough hole 11 into an axial hole 13 of the basic body 8.

At its tool-side end 3, the inner sleeve 12 is provided with an annularcollar 14 which projects radially to the outside from the outercircumference of the inner sleeve 12. As can be seen, in particular,from FIG. 4, said annular collar 14 has a two step contour inlongitudinal section, in the course of which the external diameter ofthe inner sleeve 12 first of all widens in a first step in the directionof the tool-side end 3 to a center region 15, the outer face of which isoffset parallel to the circumferential face of the inner sleeve 12.Starting from said center region 15, the annular collar 14 is thenwidened in a second step toward the tool-side end 3 to form an endsection 16 which is widened again.

The annular collar 14 corresponds with a recess 17 at the tool-side endof the through hole 11, which recess 17 is shaped in a complementarymanner with respect to said annular collar 14, with the result that theinner sleeve 12 and the clamping sleeve 9 bear sealingly against oneanother in the region of the annular collar 14 and the recess 17.Therefore, as can be seen, in particular, from FIG. 4, the interface 18which is formed in that region between the inner sleeve 12 and theclamping sleeve 9 has a profile in longitudinal section which is kinkedtwice by in each case an angle of approximately 90°. Here, the annularcollar 14 extends in the radial direction over the entire width of theclamping sleeve 9, with the result that the end section 16 of theannular collar 14 terminates, radially on the outside, approximatelyflushly with the outer circumference of the clamping sleeve 9, and theinterface 18 opens in the radially outward direction on thecircumferential face of the neck region 5. The clamping sleeve 9 and theinner sleeve 12 are brazed to one another in a pressure-tight manner inan outer part section of the interface 18. Toward the machine-side end4, the clamping sleeve 9 and the inner sleeve 12 are brazed to oneanother in a pressure-tight manner at the machine-side edge of thethrough hole 11. Here, an annular groove 20 which is made in the wall ofthe through hole 11 (FIG. 3) serves as solder flow stop in order tolimit the soldered surface.

In its interior, the inner sleeve 12 has a hole which is concentric withrespect to the chuck axis 2 and forms the receptacle 6. The inner sleeve12 is of thin-walled configuration in the region of the receptacle 6.Said thin-walled region of the inner sleeve 12 forms an expansionbushing 21 which can be deformed radially in order to clamp in the tool.The expansion bushing 21 is preferably configured integrally with theinner sleeve 12, but as an alternative can also be formed from aseparate part. An approximately hollow-cylindrical void which acts as apressure chamber 22 is formed in the region of the expansion bushing 21between the inner wall of the clamping sleeve 9 and the opposite outerwall of the inner sleeve 12. Said pressure chamber 22 merges at themachine-side end of the receptacle 6 into an annular gap 23 which islikewise formed between the inner wall of the clamping sleeve 9 and theouter wall of the inner sleeve 12. Said annular gap 23 has only anextremely small radial extent R (FIG. 6) of preferably 0.1 mm(corresponding to approximately 1/10 of the wall thickness of theexpansion bushing 21) and can therefore only be seen as such in enlargedFIGS. 4 and 6 for reasons of the resolution. In the illustrationaccording to FIG. 3, the annular gap 23 can be seen only in outline as awidened black line.

The annular gap 23 extends in the radial direction over a large part ofthe length of the clamping sleeve 9 between the pressure chamber 22 anda pressure generation unit 24 (FIG. 5), which is accommodated in thewidened annular region 10 at the machine-side end of the clamping sleeve9. Here, the annular gap 23 forms a pressure conducting system whichconnects the pressure chamber 22 fluidically to the pressure generationunit 24 and therefore makes pressure transmission possible via a liquidpressure medium F, in particular an oil, from the pressure generationunit 24 into the pressure chamber 22.

As is apparent, in particular, from FIG. 5, the pressure generation unit24 comprises a cylinder bore 25, in which a pressure piston 26 isarranged. The pressure piston 26 is guided adjustably, either directlyin the cylinder bore 25 or, as shown in FIG. 5, in a sleeve 27 which isinserted into the cylinder bore 25. The pressure piston 26 can beactuated by means of a clamping screw 28. In the embodiment shown, thepressure piston 26 and the clamping screw 28 are an integral component.Here, said component is provided with an external thread which mesheswith an internal thread of the sleeve 27. The inner end of the pressurepiston 26 carries a seal 29 made from an elastic material, in particulara rubber elastomer. Furthermore, the pressure generation unit 24comprises a filling hole 30 which extends angled away from an inner endof the cylinder bore 25 in such a way that it is approximately tangenton the annular gap 23. The filling hole 30 is therefore connectedfluidically both to the cylinder bore 25 and, via a connecting groove31, to the annular groove 23. The filling hole 30 is closed in apressure-tight manner with respect to the external world by a sphericalseal 32.

During assembly, the inner sleeve 12 is pushed into the clamping sleeve9 from the tool-side end 3. After this, the basic body 8 is attached tothe assembly which is formed from the clamping sleeve 9 and the innersleeve 12. Subsequently, in turn, the inner sleeve 12 is brazed in apressure-tight manner to the clamping sleeve 9 and the basic body 8. Asan alternative, the clamping sleeve 9 is shrunk onto the basic body 8.To safeguard the connection, which is formed between the basic body 8and the clamping sleeve 9, against rotation, a key pin 33 (FIG. 3) isadditionally inserted during mounting into aligned eccentric holes ofthe basic body 8 and the clamping sleeve 9.

Before the expansion chuck 1 is commissioned, first of all the commonvolume of the pressure cylinder 25, the filling hole 30, the annular gap23 and the pressure chamber 22 is filled completely with the liquidpressure medium F via the open filling hole 30. In order to avoid airbubbles in the pressure system, this takes place under vacuum. Afterfilling, the filling hole is closed in a pressure-tight manner by thespherical seal 32.

In order to clamp in a tool which is inserted into the receptacle 6, theclamping screw 28 and therefore the pressure piston 26 in the cylinderbore 25 can then be screwed in by means of a screwdriver. As a result,the volume of the cylinder bore 25 which is filled with the pressuremedium F is reduced, as a result of which in turn a hydrostatic pressureof typically up to 1000 bar can be applied to the pressure medium F.This pressure is transmitted via the annular gap 23 which acts aspressure conducting system as far as into the region of the pressurechamber 22. Here, the hydrostatic pressure brings about a deformation ofthe thin-walled expansion bushing 21, which deformation is directedradially onto the chuck axis 2 and by way of which the inserted tool isclamped in the receptacle 6.

In order to remove the tool out of the expansion chuck, the pressurepiston 26 is reset again by a few revolutions of the clamping screw 28,as a result of which the pressure medium F is relieved. Here, theelastically deformed expansion bushing 21 assumes its original shapeagain, with the result that the tool can be removed.

Furthermore, the expansion chuck 1 comprises an actuating journal 34(FIG. 3) for adjusting the tool axially in the receptacle 6. Theactuating journal 34 is provided with an external thread at least in apart region of its circumferential face, which external thread mesheswith an internal thread of a hole 35 at the bottom of the receptacle 6.When the tool is removed, the actuating journal 34 can be adjusted inthe axial direction by means of a screwdriver which is introduced intothe receptacle 6. Along the chuck axis 2, the expansion chuck 1 ispenetrated completely by a leadthrough which is formed by aligned holesof the inner sleeve 12, of the actuating journal 34 and of the basicbody 8. This leadthrough which is concentric with respect to the chuckaxis 2 can be used, in particular, as a coolant channel. During theoperation of the expansion chuck 1, coolant can be guided through saidcoolant channel from the machine tool into the region of the receptacle,and therefore into the region of the tool.

The invention claimed is:
 1. An expansion chuck having a tool-side endand a machine-side end, a shaft for clamping the expansion chuck in amachine tool being arranged at the machine-side end, and an expansionbushing which is surrounded by a pressure chamber being arranged at thetool-side end, which expansion bushing can be deformed radially in orderto clamp in a tool, under the action of a pressure medium which isaccommodated in the pressure chamber, the machine-side end being formedby a basic body which carries the shaft and to which, on the tool side,a clamping sleeve which delimits the outside of the pressure chamber isattached rigidly, wherein an inner sleeve which is separate both fromthe clamping sleeve and from the basic body is disposed in the interiorof the clamping sleeve and in an axial hole defined by the basic body,which inner sleeve contains the expansion bushing and delimits theinside of the pressure chamber, the inner sleeve having, at itstool-side end, a radially outwardly protruding annular collar whichoverlaps with the clamping sleeve with the result that an interfaceopens into the outer circumference of the expansion chuck, wherein thebasic body and the clamping sleeve are distinct members, initiallyformed separately and subsequently rigidly attached, the expansion chuckfurther including a pressure generation unit which is spaced apartaxially from the expansion bushing with regard to a chuck axis, and apressure conducting system for transmitting pressure from the pressuregeneration unit to the pressure chamber, the pressure conducting systembeing formed by an annular gap which is concentric with respect to thechuck axis.
 2. The expansion chuck as claimed in claim 1, wherein theannular gap is formed between the inner sleeve and the clamping sleeve.3. The expansion chuck as claimed in claim 1, wherein the pressuregeneration unit is arranged in the clamping sleeve.
 4. The expansionchuck as claimed in claim 1, wherein the pressure generation unitcomprises a cylinder bore with a pressure piston which can be adjustedtherein, and a filling hole which connects the cylinder bore to theannular gap.
 5. The expansion chuck as claimed in claim 4, wherein thepressure piston can be adjusted by means of a clamping screw.
 6. Theexpansion chuck as claimed in claim 1, wherein the radial extent of theannular gap is at most 0.2 mm.